The present invention relates to a method and a device for determining, in particular, the amount of organic carbon contained in a sample, this method also permits, if necessary, the determination of the mineral carbon content.
Various methods are already known for determining the quantity of carbon contained in liquid samples.
One of these methods, of which some embodiments are described in FRENCH PATENT Application No. 2,265,095 and in U.S. Pat. Nos. 3,296,435 and 3,530,292 consists of oxidizing a sample at a high temperature and measuring the amount of carbon dioxide which is obtained, this amount representing the total quantity of carbon contained in the sample. However, this method does not permit distinguishing between the mineral and the organic carbon in the sample.
According to another method of analyzing a liquid sample, which is described in U.S. Pat. No. 3,607,071 and BRITISH Pat. No. 1,494,906, the sample is subjected to a preliminary treatment to extract the mineral carbon therefrom.
A subsequent oxidation of the remaining fraction of the sample and the measurement of the amount of carbon dioxide so obtained permits determination of the amount of organic carbon. However, this method is time-consuming.
According to another method described in FRENCH PATENT Application No. 2,420,141 and in U.S. Pat. No. 3,672,841, the total amount of carbon contained in a sample is determined by heating the latter in an oxidizing atmosphere to at least 1000.degree. C., and measuring the amount of carbon dioxide produced during this heating step. It is assumed that by subjecting a second sample to a similar treatment at a temperature which does not exceed 600.degree. the measurement of the amount of the carbon dioxide so-produced represents the amount of organic carbon in the sample. The difference between these two results gives the amount of mineral carbon.
In practice, if the first measurement is actually representative of the total amount of carbon contained in the sample, the measurement performed on the second sample can only be valid if the sample contains no carbonate, since carbonates are decomposed under 600.degree. C., of if the carbonate amount is small compared to the amount of organic carbon. In other words, the accuracy in the determination of the amount of organic carbon is not known and the same occurs for the amount of mineral carbon which is derived from the difference between the value of the total carbon amount and the value of the amount of organic carbon.
The method for determining the organic carbon content in a geological sample which is described in BELGIAN Pat. No. 852,335 consists of pyrolyzing a sample in an inert atmosphere, measuring the amount of so-obtained benzene and deriving from this measurement, on the basis of a pre-established chart, the amount of organic carbon contained in the sample. The difficulty of this method lies in the necessity of pre-establishing a chart, and moreover, the accuracy of the results obtained by this method is low.
It is already known from FRENCH PATENT application No. 2,376,414 to pyrolyze a sample in an inert atmosphere so as to measure the sulphur compounds after oxidation of the pyrolysis products.
However this method cannot be applied to the determination of the amount of organic carbon contained in a sample of geological sediment.
With respect to these methods, the object of the present invention is to permit a faster and more accurate determination of the respective amounts of organic and mineral carbon, these results being obtained from a single sample.